Apparatus for generation of pure hydrogen for use with fuel cells

ABSTRACT

A process and apparatus are disclosed for the operation of a fuel cell to generate electric power from a feed stream comprising a hydrocarbon or an alcohol. The fuel cell comprises a proton exchange membrane which produces electric power from a hydrogen product stream which comprises essentially no carbon monoxide. The hydrogen product stream is produced from the feed stream in a novel steam reforming zone containing a steam reforming catalyst disposed in a bell-shaped catalyst zone. The bell-shaped catalyst zone is disposed over a combustion zone such that the exhaust gas from the combustion flows around the bell-shaped catalyst zone to heat the catalyst from the inside and the outside of the catalyst zone. Furthermore, the bell-shaped catalyst zone maintains a high inlet and a high outlet temperature to avoid methane slippage in the steam reforming zone. Heat for the steam reforming zone is provided by a fuel stream and at least a portion of the anode waste gas stream from the fuel cell.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Division of application Ser. No. 09/210,042 filedDec. 11, 1998, now U.S. Pat. No. 6,162,267, the contents of which arehereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a hydrogen generating apparatus and,more particularly, to a hydrogen generating apparatus which is suitablefor use as a hydrogen generating system or as a mobile electric powergeneration system when used in conjunction with a fuel cell.

BACKGROUND OF THE INVENTION

Fuel cells are chemical power sources in which electrical power isgenerated in a chemical reaction. The most common fuel cell is based onthe chemical reaction between a reducing agent such as hydrogen and anoxidizing agent such as oxygen. The consumption of these agents isproportional to the power load. Because hydrogen is difficult to storeand distribute and because hydrogen has a low volumetric energy densitycompared to fuels such as gasoline, hydrogen for use in fuel cells willhave to be produced at a point near the fuel cell, rather than beingproduced in a centralized refining facility and distributed likegasoline.

Hydrogen is widely produced for chemical and industrial purposes byconverting materials such as hydrocarbons and methanol in a reformingprocess to produce a synthesis gas.

Synthesis gas is the name generally given to a gaseous mixtureprincipally comprising carbon monoxide and hydrogen, but also possiblycontaining carbon dioxide and minor amounts of methane and nitrogen. Itis used, or is potentially useful, as feedstock in a variety oflarge-scale chemical processes, for example: the production of methanol,the production of gasoline boiling range hydrocarbons by theFischer-Tropsch process and the production of ammonia.

Processes for the production of synthesis gas are well known andgenerally comprise steam reforming, auto-thermal reforming,non-catalytic partial oxidation of light hydrocarbons or non-catalyticpartial oxidation of any hydrocarbons. Of these methods, steam reformingis generally used to produce synthesis gas for conversion into ammoniaor methanol. In such a process, molecules of hydrocarbons are brokendown to produce a hydrogen-rich gas stream.

Modifications of the simple steam reforming processes have beenproposed. In particular, there have been suggestions for improving theenergy efficiency of such processes in which the heat available from asecondary reforming step is utilized for other purposes within thesynthesis gas production process. For example, processes are describedin U.S. Pat. No. 4,479,925 in which heat from a secondary reformer isused to provide heat to a primary reformer.

The reforming reaction is expressed by the following formula:

CH₄+2H₂O→4H₂+CO₂

where the reaction in the reformer and the reaction in the shiftconverter are respectively expressed by the following formulae (1) and(2)

CH₄+H₂O→CO+3H₂

CO+H₂O→H₂+CO₂

In the conventional hydrogen generating apparatus, an inert gas heatedin a reformer is made to flow through a process flow path so as to raisetemperatures of the shift converter and the heat exchangers which aredownstream from the reformer.

U.S. Pat. No. 5,110,559 discloses an apparatus for hydrogen generationwhich includes a reformer and a shift converter each incorporating acatalyst wherein, during the start-up of the apparatus, reformercombustion gas is introduced to a shift converter jacket surrounding theshift converter catalyst to heat the shift converter to provide astart-up or temperature rise of the reformer system.

U.S. Pat. No. 4,925,456 discloses a process and an apparatus for theproduction of synthesis gas which employs a plurality of double pipeheat exchangers for primary reforming in a combined primary andsecondary reforming process. The primary reforming zone comprises atleast one double-pipe heat exchanger-reactor and the primary reformingcatalyst is positioned either in the central core or in the annulusthereof. The invention is further characterized in that the secondaryreformer effluent is passed through which ever of the central core orthe annulus is not containing the primary reforming catalystcounter-currently to the hydrocarbon-containing gas stream.

U.S. Pat. No. 5,181,937 discloses a system for steam reforming ofhydrocarbons into a hydrogen rich gas which comprises a convectivereformer device. The convective reformer device comprises an outer shellenclosure for conveying a heating fluid uniformly to and from a coreassembly within the outer shell. The core assembly consists of amultiplicity of tubular conducts containing a solid catalyst forcontacting a feed mixture open to the path of the feed mixture flow suchthat the path of the feed mixture flow is separated from the heatingfluid flow in the outer shell. In the process, an auto-thermal reformerfully reforms the partially reformed (primary reformer) effluent fromthe core assembly and supplies heat to the core assembly by passing thefully reformed effluent through the outer shell of the convectivereforming device.

Fuel cells are chemical power sources in which electrical power isgenerated in a chemical reaction. The most common fuel cell is based onthe chemical reaction between a reducing agent such as hydrogen and anoxidizing agent such as oxygen. The consumption of these agents isproportional to the power load. Because hydrogen is difficult to storeand distribute and because hydrogen has a low volumetric energy densitycompared to fuels such as gasoline, hydrogen for use in fuel cells willhave to be produced at a point near the fuel cell, rather than beproduced in a centralized refining facility and distributed likegasoline. Polymers with high protonic conductivities are useful asproton exchange membranes (PEM's) in fuel cells. Among the earliestPEM's were sulfonated, crosslinked polystyrenes. More recentlysulfonated fluorocarbon polymers have been considered. Such PEM's aredescribed in an article entitled, “New Hydrocarbon Proton ExchangeMembranes Based on Sulfonated Styrene-Ethylene/Butylene-Styrene TriblockCopolymers”, by G. E. Wnek, J. N. Rider, J. M. Serpico, A. Einset, S. G.Ehrenberg, and L. Raboin presented in the Electrochemical SocietyProceedings (1995), Volume 95-23, pages 247 to 251.

The above processes generally relate to very large industrial facilitiesand the techniques for integrating the steps of converting thehydrocarbon or alcohol feed stream may not be useful in compact,small-scale hydrogen-producing units to power a transportation vehicleor to supply power to a single residence. One of the problems of largehydrogen facilities is the problem of methane slippage in steamreforming reactors. “Methane slippage” is a term used to describe areduction in the methane conversion across the reforming reactor.Generally, the equilibrium conversion of methane to carbon oxides andhydrogen that is achieved in the reforming reactor increases withtemperature. Consequently, a reduction in the reactor outlet temperaturecorresponds to a lower conversion of methane, or a methane slippage.Methane slippage reduces the overall production of hydrogen and hencethe efficiency of the process. Methane slippage can create problems indownstream equipment such as in an oxidation step used to remove traceamounts of carbon monoxide from the hydrogen stream before passing thehydrogen stream to the fuel cell.

It is the objective of this invention to provide a compact apparatus forgenerating hydrogen from available fuels such as natural gas,hydrocarbons, and alcohols for use in a fuel cell to generate electricpower.

It is an objective of this invention to provide an integrated fuel celland hydrogen production system which is energy and hydrogen efficient.

It is an objective of the present invention to provide an apparatus forthe steam reforming of methane which mitigates the methane slippageproblem and achieves a more uniform temperature throughout the steamreforming zone.

SUMMARY OF THE INVENTION

The steam reforming apparatus of the present invention which has acombustion zone positioned inside a steam reforming zone whereby thesteam reforming zone is heated by radiation from the combustion zone andby convection from exhaust gases contacting the inside and the outsideof the steam reforming zone provides a simple and efficient system forproducing hydrogen from a hydrocarbon or an alcohol stream. By disposingthe steam reforming catalyst in a dome shaped, or bell shaped catalystzone surrounding a combustion zone, the steam reforming zone can bemaintained at effective steam reforming conditions which on thissmall-scale unit minimizes the methane slippage problem of conventionalapproaches which use a fixed bed reactor or only heat the catalyst fromone side. Furthermore, the closed-end top of the bell-shaped catalyst,located above the combustion zone assures that the outlet temperature ofthe steam reforming reaction zone is maintained at a temperatureessentially equal to or greater than the steam reforming reaction zoneinlet temperature. The use of a simple burner in the combustion zonewith provision to burn both the methane fuel and the anode wastegas—which comprises a significant amount of hydrogen—achieves a betteroverall energy balance in providing heat to the endothermic steamreforming reaction. The anode waste gas stream is injected into a flamezone provided by the combustion of the methane fuel stream. The furtheruse of the cathode waste gas provides a simplified method of controllingelectrical demand induced variations in the combustion zone temperatureand the overall energy balance without venting an undesirable steamplume from the fuel cell.

An unexpected benefit of the recycle of a portion of the cathode wastegas to be burned in the combustion zone is that the chance of a plume ofcondensation forming in the exhaust gas of the process is reduced. Aplume of condensation is formed if a warm humid gas is released to theatmosphere at a temperature that is close to the dew point. When the gasmeets colder air the moisture is condensed, giving a visible plume,which is undesirable as the public associates such plumes with smoke andpollution.

For an electrical output of about 7 kW, the present invention required anatural gas throughput of about 2.4 normal cubic meters per hour (about1.4 standard cubic feet per minute) thus providing an overall energyefficiency of about 30 percent.

In one embodiment, the present invention comprises a process for thegeneration of hydrogen for producing electric power from a fuel cell. Afeed stream and a water stream are admixed to provide a feed admixtureand the feed admixture is passed to a heat exchange zone to heat thefeed admixture by indirect heat exchange to provide a heated admixture.The heated admixture at effective steam reforming conditions is passedto a feed inlet of a steam reforming zone at an inlet temperature toconvert the heated feed admixture and produce a steam reforming effluentstream comprising hydrogen and carbon monoxide. The steam reforming zonecomprises a compartment provided by a middle space within one or morehollow walls which defines a vessel. The vessel is vertically alignedand has an open-end base and a closed-end top to define a catalyst zonehaving an inlet into the compartment about the open-end base and anoutlet out of the compartment about the closed-end top. The vessel hasan inside surface defining an interior, an upper interior adjacent tothe closed-end top, and an outside surface. The compartment contains asteam reforming catalyst. A fuel gas mixture is burned in the presenceof a first oxygen-containing stream within a combustion zone defined bya combustion tube that contains a flame. The combustion tube extendsvertically within the interior of said vessel to provide radiant heat tothe steam reforming zone and to produce a fuel exhaust stream. The fuelexhaust stream is circulated downwardly from the upper interior of thevessel over the inside surface of the vessel and upwardly over theoutside surface of the vessel to heat the catalyst zone by convectionand to maintain the steam reforming catalyst at effective steamreforming conditions. The steam reforming effluent stream is withdrawnfrom the outlet at an outlet temperature that differs by no more thanabout 50° C. from the inlet temperature.

In another embodiment, the present invention is an apparatus forgenerating hydrogen for producing electric power from a fuel cell. Theapparatus comprises the following elements. A substantially closed outervessel defines an interior chamber and comprises insulated walls and abase. An inner vessel within the interior chamber has a closed-end top,an open-end bottom and is defined by one or more hollow walls. Themiddle space within the hollow provides a compartment for retainingcatalyst. The inner vessel surrounds a combustion zone. A burner isfixed with respect to the base and is positioned within the combustionzone to provide a flame zone. An anode waste gas conduit is disposed inthe combustion zone to provide for the injection of anode waste gasdirectly into the flame zone. A burner tube is fixed with respect to thebase. The burner tube extends vertically above the base to surround theburner. A feed distributor is fixed with respect to the inner vessel anddefines a plurality of ports distributed about the open-end bottom forcommunication with the compartment. A feed conduit is in fluidcommunication with the feed distributor. A reforming effluent outlet isdefined by the closed-end top of the interior vessel and is in fluidcommunication with the compartment. A fuel exhaust outlet is defined bythe top of the outer vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block flow diagram illustrating the process of thepresent invention.

FIG. 2 is an isometric drawing providing an interior view of the steamreforming zone of the present invention.

FIG. 3 illustrates the top plate of the feed distributor of the presentinvention.

FIG. 4 is an isometric drawing showing a cross section of the shiftreaction zone of the present invention.

FIG. 5 is a chart showing calculated radial temperature profiles of theprior art.

FIG. 6 is a chart showing calculated radial temperature profiles of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Conventional steam reforming plants are able to achieve high efficiencythrough process integration; that is, by recovering heat from processstreams which require cooling. In the conventional large-scale plantthis occurs in large heat exchangers with high thermal efficiency andcomplex control schemes. In the present invention for the production ofhydrogen for fuel cells it is desired to reach a high degree of processintegration, with minimal equipment in order to reduce the size of theplants and the complexity of the control scheme.

The process of the current invention uses a hydrocarbon-containing gassuch as natural gas as a feedstock. Natural gas, and similar hydrocarbonstreams generally contain impurities such as sulfur in the form ofhydrogen sulfide, mercaptans, and sulfur oxides which must be removedprior to introducing the feedstock to the steam reforming zone. Theremoval of sulfur from the hydrocarbon feedstock may be accomplished byany conventional means including adsorption, chemisorption, andcatalytic desulfurization. In order to reduce the overall size of thehydrogen generation equipment, chemisorption with a material such aszinc oxide is preferred. The desulfurization operation will generallytake place at effective conditions including a desulfurization pressureof between about 100 to about 1000 kPa. Preferably the desulfurizationoperation is carried out at a desulfurization pressure of between 200and 300 kPa. Preferably, the desulfurization operation is carried out ata desulfurization temperature less than about 300° C., and morepreferably, the desulfurization operation is carried out at adesulfurization temperature between about 50° C. and about 300° C.Preferably, the concentration of sulfur in the desulfurized feedstockwill be less than about 10 ppm-mol, and more preferably theconcentration of sulfur in the desulfurized feedstock will be less thanabout 1 ppm-mol. The feedstock is divided into two separate streams, thereforming feed stream and a burner fuel stream. The reforming feedstream is preferably desulfurized to provide a desulfurized feed stream.Optionally, the entire feedstock is desulfurized prior to dividing thefeedstock into a desulfurized feed stream and a burner fuel stream whichis also desulfurized.

Water is required by the steam reforming process for use as a reactantand as a cooling medium. In addition, the hydrogen product must bedelivered to the fuel cell as a wet gas to avoid drying out the PEMmembrane in the fuel cell. The water used in the steam reforming processpreferably will be deionized to remove dissolved metals includingsodium, calcium, lead, copper, arsenic, and anions such as chloride ionsto prevent pre-mature deactivation of the steam reforming catalyst orother catalytic materials contained in the fuel cell, the water gasshift catalyst, or the carbon monoxide oxidation catalyst. Thedeionization of the water to be used in the process may be accomplishedby any conventional means.

The steam reforming zone contains a steam reforming catalyst.Preferably, the steam reforming catalyst includes nickel with amounts ofnoble metal, such as cobalt, platinum, palladium, rhodium, ruthenium,iridium, and a support such as magnesia, magnesium aluminate, alumina,silica, zirconia, singly or in combination. More preferably, the steamreforming catalyst can be a single metal such as nickel or a noble metalsupported on a refractory carrier such as magnesia, magnesium aluminate,alumina, silica, or zirconia, singly or in combination, promoted by analkali metal such as potassium. Most preferably, the steam reformingcatalyst comprises nickel supported on alumina and promoted by an alkalimetal such as potassium. The steam reforming catalyst can be granularand is supported within the steam reforming zone within a bell-shapedcatalyst zone between an inner wall and an outer wall of the bell-shapedcatalyst zone. Preferably the steam reforming zone is operated ateffective reforming conditions including a reforming temperature ofbetween about 650° C. and about 950° C. and a reforming pressure ofbetween about 100 and 350 kPa.

The steam reforming reaction is an endothermic reaction and requiresheat to maintain the equilibrium in the direction of converting methaneor hydrocarbon to produce hydrogen. Heat is supplied to the steamreforming zone by burning a burner fuel stream in a combustion zonewhich transfers heat to the steam reforming reaction zone by radiationand convection. An oxygen-containing gas such as air and burner fuel gasmixture is contacted at effective combustion conditions to maintain acombustion zone temperature of between about 1200° C. and about 2000° C.The fuel and air are mixed in proportions to assure optimum combustion.Normally the mass flow rate of the fuel and air supplied to the burneris variable and governed thermostatically according to sensed combustionzone temperature. In the operation of the steam reforming zone inconjunction with the fuel cell of the present invention, the combustionzone temperature, and hence the amount of heat provided to the steamreforming reaction can be controlled by employing a portion of the anodewaste gas which comprises hydrogen, nitrogen, and carbon dioxide toenhance the heating value of the burner fuel gas stream. The heatcontent of the anode waste gas, comprising hydrogen has a heat contenton a molar basis significantly greater than the burner fuel gas streamand must be introduced into the flame zone above the burner. The flamezone is contained within a burner tube such as those described in U.S.Pat. No. 4,157,241 which is hereby incorporated by reference. Thetemperature of the flue gas, monitored downstream of the flame zone, ina position shielded from radiant heat of the flame is employed to adjustthe flow of air to the burner. A carbon monoxide monitor may also beplaced in the flue gas stream to monitor the carbon monoxide content ofthe flue gas and adjust the air flow to the burner to maintain acondition of excess oxygen. In this manner, the hydrogen generated bythe steam reforming reaction zone and not consumed by the fuel cell isnot recycled to the reforming zone, but is burned to provide thermalintegration of the overall process. Preferably, at least 60 mole percentof the anode waste gas stream is combined with the burner fuel stream,and more preferably at least 80 percent of the anode waste gas stream iscombined with the burner fuel stream, and most preferably at least 95percent of the anode waste gas stream is combined with the burner fuelstream.

As a further means of controlling the temperature of the combustionzone, a portion of the cathode waste gas stream withdrawn from the fuelcell, which comprises nitrogen and a reduced oxygen content relative toair is admixed with the burner fuel. Preferably, less than about 20 molepercent of the cathode waste gas stream is combined with theoxygen-containing stream, and more preferably, between about 5 and about20 percent of the cathode waste gas stream is combined with theoxygen-containing stream, and most preferably, between about 5 and about15 percent of the cathode waste gas stream is combined with theoxygen-containing stream to control the temperature of the combustionzone. The addition of cathode waste gas to the burner during theoperation of the process serves to reduce the efficiency of thecombustion and thereby lower the temperature of the combustion zone.

The effluent withdrawn from the steam reforming zone comprises hydrogen,carbon dioxide, carbon monoxide, water, and methane. It is an objectiveof the process of the invention to maintain a low level of methane inthe steam reforming effluent. Preferably, the steam reforming effluentwill contain less than about 1 mole percent methane, and morepreferably, the steam reforming effluent will contain less than about0.5 mole percent methane. In order to obtain these very low methanelevels, it is required to maintain a high exit temperature from thesteam reforming zone. It is believed that this objective is accomplishedby heating the steam reforming catalyst contained in the bell-shapedcatalyst zone by direct radiation from the combustion tube, byconvection of the fuel exhaust gases on the inside of the bell-shapedcatalyst zone, and by convection of the fuel exhaust gases on theoutside of the bell-shaped catalyst zone. It is believed that by thesemeans the temperature profile radially at any point in the catalyst zonewill be significantly more uniform than catalyst beds heated from onlyone side. In addition, by maintaining a high steam reforming zone inlettemperature and a high outlet temperature, the equilibrium of the steamreforming reaction can be directed to the essentially completeconversion of methane or other hydrocarbon. By the term “essentiallycomplete conversion”, it is meant that more than 95 percent of thehydrocarbon in the steam reforming zone feedstock is converted to wateror hydrogen and carbon oxides.

The steam reforming effluent comprises about 5 to about 15 mole percentcarbon monoxide. Because carbon monoxide acts as a poison to the PEMfuel cell, the carbon monoxide must be removed to produce a hydrogenproduct gas. This is accomplished by passing the steam reformingeffluent to a series of shift reaction zones which exothermically reactthe carbon monoxide over a shift catalyst in the presence of an excessamount of water to produce carbon dioxide and hydrogen. In the presentinvention, the steam reforming effluent is passed to a first water sprayzone to reduce the temperature of the steam reforming effluent to aneffective high temperature shift temperature of between about 400° C. toabout 450° C. and passing the cooled steam reforming effluent over ahigh temperature shift catalyst to produce a high temperature shifteffluent. The high temperature shift catalyst is selected from the groupconsisting of iron oxide, chromic oxide, and mixtures thereof. The hightemperature shift effluent is passed to a second water spray zone toreduce the temperature of the high temperature shift effluent to atemperature of between about 180° C. and about 220° C. to effectiveconditions for a low temperature shift reaction and to provide a cooledhigh temperature shift effluent. The cooled high temperature shifteffluent is passed to a low temperature shift zone and contacted with alow temperature shift catalyst to further reduce the carbon monoxide andproduce a low temperature shift effluent. The low temperature shiftcatalyst comprises cupric oxide (CuO) and zinc oxide (ZnO). Other typesof low temperature shift catalysts include copper supported on othertransition metal oxides such as zirconia, zinc supported on transitionmetal oxides or refractory supports such as silica or alumina, supportedplatinum, supported rhenium, supported palladium, supported rhodium, andsupported gold. The direct water contacting of the steam reformingeffluent and the high temperature shift effluent results in theproduction of a water saturated hydrogen product. This is desired toprevent damage to the PEM membrane in the fuel cell. Preferably adispersion zone is provided between the first water spray zone and thehigh temperature shift zone and between the second water spray zone andthe low temperature shift zone to facilitate the dispersion of the waterspray with steam reforming effluent and the high temperature shifteffluent, respectively. The low temperature shift reaction is a highlyexothermic reaction and a portion of the heat of the low temperatureshift reaction is removed by indirect heat exchange with a water streamto produce a preheated water stream. The preheated water stream at atemperature of about 100° C. to about 150° C. is admixed with thedesulfurized reforming feed stream to further conserve thermal energy.The low temperature shift effluent comprising less than about 0.5 molepercent carbon monoxide is passed to a carbon oxide oxidation zone ateffective oxidation conditions and contacted with an oxidation catalystto produce a hydrogen product gas stream comprising less than about 40ppm-mole carbon monoxide. Preferably, the hydrogen product gas streamcomprises less than about 10 ppm-mole carbon monoxide, and morepreferably, the hydrogen product gas stream comprises less than about 1ppm-mole carbon monoxide. The heat of oxidation produced in the carbonoxide oxidation zone is removed in a conventional manner by cooling thecarbon oxide oxidation zone in a conventional manner such as with awater jacket and a cooling water stream.

The hydrogen product gas comprising water at saturation and at atemperature less than about 100° C. is passed to the anode side of afuel cell zone comprising at least one proton exchange membrane (PEM).The PEM membrane has an anode side and a cathode side, and is equippedwith electrical conductors which remove electrical energy produced bythe fuel cell when an oxygen-containing stream is contacted with thecathode side of the PEM membrane. It is required that the PEM membranebe kept from drying out by maintaining the hydrogen product stream atsaturation conditions. It is also critical that the PEM membrane bemaintained at a temperature less than 100° C. The PEM membrane is onlyabout 70 percent efficient in its use of the hydrogen product stream andas a result, the fuel cell produces an anode waste gas comprisinghydrogen and a cathode waste gas comprising oxygen. The anode waste gasproduced by the present invention comprises less than about 50 molepercent hydrogen, and the cathode waste gas comprises less than about 15mole percent oxygen.

The use of anode waste gas as a fuel for the process is disclosed byU.S. Pat. No. 4,746,329 when it is mixed with air and combusted toprovide heat to a reforming zone. On the surface it appears to beadvantageous to use the anode waste gas in this manner because the heatof combustion of the anode waste gas can be recovered; however, morecareful consideration of the overall process performance reveals severalproblems. The combustion of anode waste gas in the combustion zoneproduces less flue or exhaust gas from the burner, but the burning ofthe anode waste gas produces high flame temperatures than from burningfuel gas. In the present invention the flue gas provides heat to thesteam reforming reaction zone by convection from the flue exhaust gasesand by high temperature radiation from the flame zone. Because of therelatively high proportion of heat that is released at high flametemperature, problems can result. In fact, when the temperature in theflame zone becomes excessive, the process equipment can be damaged.Table 1 shows the efficiency of the process, defined as the lowerheating value of the net hydrogen produced (i.e., hydrogen producedminus hydrogen returned in the form of anode waste gas) divided by thelower heating value of the methane expressed as a percent, and thehydrogen utilization of the fuel cell (i,e., the percent of the hydrogenwhich is converted in the fuel cell).

TABLE 1 Process Efficiency vs. Hydrogen Utilization Hydrogen NetHydrogen Utilization, % Efficiency, % 60 56 70 62 80 63 90 65 100 66

Because the overall process efficiency is lower at lower values ofhydrogen utilization, the more anode waste gas produced, the lessefficient is the process. It is believed that for an improved operation,the formation of anode waste gas should be minimized and that thehydrogen utilization of the fuel cell should be increased. Furthermore,the concentration of hydrogen in the anode waste gas will vary dependingupon the electrical load drawn from the fuel cell. This variationdynamically changes the heating value of the anode waste gas which canhave a deleterious effect on process performance, particularly when theanode waste gas is used as the main component of the fuel for theprocess. Variation in the hydrogen content of the fuel also causesvariation in the flame length, which can lead to loss of the flame, withserious implications for process safety. Thus, the direct disposal ofthe anode waste gas directly into a burner as fuel is fraught withdifficulty. The control of the flame is difficult to maintain whichresults in wide temperature variations in the steam reforming zone.

According to the present invention, the problems associated with burningthe anode waste gas can be overcome by the following means. The primaryburner feed comprises a fuel stream of natural gas and anoxygen-containing/ or oxidant stream containing an excess of air. Theanode waste gas is provided directly into the flame zone formed bycombustion of a burner fuel comprising natural gas. This ensures thatthere is always a steady flame to light off the hydrogen, even when thehydrogen concentration fluctuates. The performance can be furtherimproved by replacing a portion of the oxygen-containing stream such asair with a portion of the cathode waste gas. The cathode waste gas isenriched in nitrogen relative to oxygen and saturated with water at atemperature of about 80° C. The cathode waste gas, therefore, has a highthermal capacity and low oxidation power. Use of the cathode waste gasas a secondary oxygen-containing stream considerably lowers the flametemperature. The amount of cathode waste gas produced is relativelyconstant, owing to the high concentration of nitrogen in air. Accordingto the invention, the cathode waste uses a portion of this gas asoxidant, and therefore, serves to dampen variations in the flame lengthand flame temperature that would be experienced as a result offluctuations in hydrogen concentration in the anode waste gas. It is notadvisable to recycle all of the cathode waste gas to the burner, astaught by EP 199 878A2, as this will cause excessive lowering of theflame temperature, as illustrated in Table 2, hereinbelow withcalculated flame performance.

TABLE 2 Effect of Cathode Waste Gas Recycle on Flame Temperature %Cathode Waste Gas 0 5 10 15 20  50 100 Recycled Stoichiometric Flame1680 1534 1423 1318 1235 881 551 Temperature, ° C.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to FIG. 1, a desulfurized fuel stream in line 10 iscombined with a water stream in line 40 and passed to a thefeed/effluent exchanger 88 wherein the desulfurized fuel stream isadmixed with the water stream to form a fuel/water in admixture 10′ asthe fuel/water admixture 10′ is heat exchanged with a fuel exhauststream in line 34 to at least partially heat the fuel/water admixturestream 10′. The feed/effluent exchanger 88 comprises a multiple passexchanger which permits the water stream to be admixed with the fuelstream as the admixture is heated by indirect exchange with fuel exhauststream. The fuel/water admixture stream is withdrawn in line 12 and acooled fuel exhaust stream is withdrawn in line 36 and released to theatmosphere. The fuel/water admixture stream in line 12 at effectivesteam reforming conditions is passed to a feed inlet of a steamreforming zone 21. The steam reforming zone 21 comprises a hollowinsulated chamber 30, containing a burner 32, a burner tube 22,comprising a ceramic or metal tube surrounding the burner 32, abell-shaped catalyst zone having a closed-end top, or reactor outlet 24′from which reforming reactor effluent is removed and an open-end basewhich functions as the steam reforming reaction zone inlet. Thebell-shaped catalyst zone contains a reforming catalyst selective forthe steam reforming of the feed water admixture. The bell-shapedcatalyst zone is formed by an interior wall 26 and an exterior wall 28defining an interior space and contains a steam reforming catalyst 20between the inner wall 26 and the exterior wall 28 of the bell-shapedcatalyst zone. It is preferred that the reforming catalyst notcompletely fill the interior space of the bell-shaped catalyst zone, butthat the interior space contain an inert zone 18 comprising an open zoneor an inert catalyst support material disposed at the open-end base ofthe bell-shaped catalyst zone. When the feed admixture contact the steamreforming catalyst, the endothermic nature of the reaction immediatelydrops the temperature at the reaction zone inlet. By extending thereaction zone inlet with an inert zone which is from about 1 to about 15percent of the length of the reaction zone, a more stable reaction zoneinlet temperature is maintained. The combustion tube 22 is disposedconcentrically between the burner 32 and the inner wall 26 of thebell-shaped catalyst zone and forms a combustion zone 33 containing aflame zone 35 wherein a fuel stream entering from line 80 and anoxygenate-containing stream in line 85 are combusted to produce the fuelexhaust stream. The fuel exhaust stream exits the combustion zone 33through the top of the burner tube 22 and enters an inner chamber 21 aformed by an inner wall 26 of a bell-shaped catalyst zone and the burnertube 22. The bell-shaped catalyst zone completely surrounds and enclosesthe burner tube 22. In its simplest form the base of the catalyst zoneis disposed on a feed distributor 16 which directs the fuel/wateradmixture to the base of the catalyst zone at the open-end of thebell-shaped catalyst zone. The fuel/water admixture in line 12 is passedthrough conduit 14 and the feed distributor 16 to react with the steamreforming catalyst 20 to produce a reforming reactor effluent stream.The reforming reactor effluent stream is removed from the bell-shapedcatalytic zone via conduit 24, which is in fluid communication with thebell-shaped catalyst zone and which is located at the top or outlet ofthe bell-shaped catalytic zone. The fuel exhaust stream in the innerchamber 21 a exchanges heat with the inner wall 26 to provide heat tothe steam reforming catalyst 20 from the inside of the bell-shapedreaction zone. As the fuel exhaust exits the inner chamber 21 a, and ispassed under the feed distributor 16 into the outer space 21 b formedbetween the outer wall of the catalyst zone 28 and the insulated wall 30of the steam reforming zone 21, additional heat is provided to thereforming catalyst from the outer wall of the bell-shaped catalyst zone.Thus, the steam reforming catalyst 20 is heated both from the insidewall 26 and the outside wall 28 by the fuel exhaust stream to maintaineffective steam reforming conditions and to provide an even heatdistribution, radially through the bell-shaped catalyst zone. The fuelexhaust stream leaves the steam reforming zone 21 via conduit 29.Preferably conduit 29 is disposed in close proximity to conduit 24. Thesteam reforming reaction inside the bell-shaped catalyst zone is anendothermic reaction. By passing the fuel exhaust stream on both sidesof the catalyst zone and providing the burner tube which extends thecombustion zone to a point approaching the closed-end top, or outlet ofthe bell-shaped catalyst zone, a concave temperature profile from theinlet of the reaction zone to the outlet of the bell-shaped catalystzone is established which is characterized by a first peak temperatureat the inlet of the bell-shaped catalyst zone and a second peaktemperature at the outlet of the bell-shaped catalyst zone. It isbelieved that this concave temperature profile, particularly a hot exittemperature, maintains the level of methane conversion to hydrogen atthe steam reforming reactor outlet. In addition, the fuel exhaust streamheats the fuel/water admixture in conduit 14 by indirect heat exchangewith the fuel/water admixture. The reforming reactor effluent iswithdrawn from conduit 24 at the closed-end top of the bell-shapedcatalyst zone as a reforming reactor effluent stream and the reformingreactor effluent stream is passed in line 42 to a shift reaction zone44. The shift reaction zone 44 comprises a high temperature shiftreaction zone 48 and a low temperature shift reaction zone 50 whereinthe reforming reactor effluent undergoes a water gas shift reaction tofavor the production of hydrogen. A second water stream in line 46 isintroduced to the shift reaction zone 44 via line 46 at an upper portionof the shift reaction zone 44. Preferably, the second water stream inline 46 is admixed with the reforming reactor effluent by spraying thesecond water stream through a first water spray zone 44 a and contactingthe resulting first water/effluent admixture at effective hightemperature shift conditions with a high temperature shift catalyst toproduce a high temperature shift effluent. The high temperature shifteffluent is contacted with a third water stream in line 54 in a secondwater spray zone 44 b to form a high temperature shift/water admixtureand the high temperature shift/water admixture is passed to a lowtemperature shift reaction zone 50. The low temperature shift reactionis an exothermic reaction. Cooling of the low temperature shift reactionzone 50 is provided by the third water stream in line 54. If required inemergency conditions, additional cooling is provided by a cooling coil56 through which a fourth water stream in line 52 is passed to maintainthe low temperature shift reaction at effective conditions to produce alow temperature shift effluent stream. A fifth water stream is withdrawnin line 53 and passed to a drain. The low temperature shift effluentstream comprising hydrogen, carbon monoxide, carbon dioxide, andnitrogen is passed via line 60 to a shift effluent cooler 61. In theshift effluent cooler the shift effluent stream in line 60 is cooled toeffective oxidation conditions such as oxidation temperature 40° C. to100° C. and an oxidation pressure less than about 2 atmospheres toproduce an oxidation zone feed stream in line 60′ by indirect heatexchange with an deionized water stream in line 40′. A preheated waterstream which is now heated and partially vaporized is withdrawn from theshift effluent cooler 61 in line 40. The oxidation zone feed stream inline 60′ is passed to a carbon monoxide oxidation zone 64. The carbonmonoxide oxidation zone contains a carbon oxide oxidation catalyst 66comprised of a noble metal selected from the group consisting ofplatinum, palladium, ruthenium, gold, rhodium, iridium, and mixturesthereof supported on alumina or some other suitable binder and is cooledin a conventional manner, shown here as with a water jacket 68 whichpermits a cooling water stream in line 62 to flow through the waterjacket or cooling coil to maintain the carbon oxide oxidation catalystat effective carbon oxide oxidation conditions to produce a hydrogenproduct stream in line 71 comprising hydrogen and less than about 100ppm carbon monoxide. Water heated in the process of cooling the carbonmonoxide oxidation zone 64 is removed as a heated water stream in line70. The hydrogen product stream in line 71 is passed to a PEM fuel cell72 which is maintained at a temperature of less than about 100° C. by aconventional cooling system (not shown). The hydrogen product streamcomprising essentially pure hydrogen is contacted with the anode side ofat least one PEM membrane 90 while the cathode side of the PEM membraneis contacted with an oxygen-containing stream such as air in line 76.The PEM membrane produces electrons which are removed by electricalconnections 95 to provide electrical energy 100. A plurality of PEMmembranes may be connected in series or in parallel to obtain thedesired amount of electrical energy. In the process of generatingelectricity with the PEM membrane, a portion of the hydrogen productstream is not consumed and is recovered as an anode waste gas stream inline 74. The anode waste gas stream is passed to the combustion zone 33wherein it is injected into the flame zone 35. Similarly, a portion ofthe oxygen-containing stream in line 76 is recovered as a cathode wastegas stream in line 78. The anode waste gas which comprises hydrogen hasa variable heat content which is generally higher than natural gas andwhich is effectively employed to enrich the natural gas which issupplied to burner 32 via line 80. The anode waste gas is injected intothe flame zone 35 to provide a more reliable operation. The cathodewaste gas which is somewhat depleted in oxygen relative to air isgenerally vented to the atmosphere via lines 78 and 86, but a portion ofthe cathode gas stream in line 78 may be employed to control the heatdelivered to the steam reforming zone 21 by admixing at least a portionof the cathode waste gas stream in lines 78 and 84 with a freshoxygen-containing stream in line 82 prior to passing theoxygen-containing stream in line 85 to the burner 32. A shieldedtemperature sensor located in the combustion zone 33 may be effectivelyemployed to direct the amount of cathode waste gas in line 84 passed tothe burner 32 via lines 84 and 85 to maintain effective stream reformingconditions and avoid overheating the steam reforming catalyst.

FIG. 2 shows an isometric sectional view of a steam reforming zone 200.The steam reforming zone comprises a hollow insulated chamber havinginsulated walls 202 and a base 201 defining an interior chamber space.Within the interior chamber space and rigidly disposed on the base 201of the steam reforming zone is a burner 216. The burner 216 is suppliedwith fuel and air by means of a fuel conduit 240 and an air conduit 212in closed communication with the burner and being rigidly attached tothe burner 216 from the exterior side of the base of the streamreforming zone 200. An anode waste gas conduit 230 disposed in thecombustion zone 225 provides a means for supplying the anode waste gasstream directly into the flame zone 227 in the combustion zone 225. Acylindrical burner tube 214 made of metal or ceramic material isdisposed on the base of the steam reforming zone fully surrounding theburner 216 and extending above the base of the steam reforming zone 200to define a combustion zone. Preferably, the burner tube is fabricatedof metal selected from the group consisting of a high nickel alloy, asuper alloy, or a combustor alloy including, but not limited to, alloysselected from the group consisting of 214, 601, 600, 230, 617, 333, 671,800H, RA330, 310, HK40, and H160, or a ceramic material such as alumina,silicon carbide, aluminum nitride, silicon nitride, or sialon. Morepreferably, the burner tube is fabricated from a metal selected from thegroup consisting of 214 and RA330, or a ceramic material comprisingsilicon carbide. The shape of the burner tube may be altered to balancethe ratio of radiant heat to convection heat transferred to the reactor.For example, the burner tube 214 may be slotted or may contain aplurality of holes to increase the amount of direct radiation; theburner tube may be coated to emit a particular range of radiationfrequencies adsorbed by the exhaust gas, or transparent to the exhaustgas; the burner may comprise a concave or convex shape to directradiation to a specific point of the interior wall of the bell-shapedcatalyst zone; or the burner tube may comprise deflector shields toadsorb radiation and to provide heat to the exhaust gas by convection. Abell-shaped catalyst zone 220 having an exterior wall 208 and aninterior wall 207, an outlet 206 at the closed-end top of the bell andan inlet at the open-end base of the bell, opposite, is disposed on afeed distributor 210 to form a bell-shaped catalyst zone. Preferably,the bell-shaped reactor is fabricated from a metal such as a high nickelalloy, a super alloy, or a combustor alloy including, but not limited toalloys 800H, HK40, and RA330. More preferably, the bell-shaped reactoris fabricated from a metal alloy selected from the group consisting of800H, 214, and HK40. The structure of the feed distributor 210 is shownin FIG. 2 and FIG. 3 with the same reference numbers. The feeddistributor is disposed at the bottom or inlet of the bell-shapedcatalyst zone and is in closed communication with the exterior andinterior walls 208 and 207 of the bell-shaped catalyst zone to separatethe interior of the bell-shaped catalyst zone from the interior chamberspace. A plurality of assembly supports 222 disposed on the feeddistributor 210 provide support for the feed distributor above the base201 of the steam reforming zone 200 to permit the flow of exhaust gasesfrom the burner 216 to flow under the feed distributor 210 and on bothsides of the bell-shaped catalyst zone. The assembly supports 222 may berigidly attached to the base 201 of the steam reforming zone 200, orrigidly attached to the insulated walls 202 of the steam reforming zone200, or attached to a combination of the insulated walls and the base ofsteam reforming zone 200. A cylindrical feed distributor 210 has a topsurface 218′ and a bottom surface. The top surface 218′ has a pluralityof openings 218, which may be holes or raised nipples, to place the feeddistributor 210 in fluid communication with the interior of thebell-shaped catalyst zone. An inert zone 219, containing an inertcatalyst support material such as glass, sand, or ceramic material, orcontaining no material is provided between the feed distributor and thecatalyst in the bell-shaped catalyst zone to improve the distribution ofthe fuel/water admixture to the catalyst zone and to provide a finalheating zone prior to contacting the fuel/water admixture with thecatalyst. A feed conduit 209 is disposed in the interior chamber spaceand rigidly attached to the feed distributor 210. The feed conduit 209is in fluid communication with the feed distributor 210. The passage ofexiting fuel exhaust from the burner 216 through the interior chamberspace and on the outside surface of the feed conduit further heats thefeed/water admixture. The outside surface of the feed conduit may be anextended surface 209′ having fins or surface extensions to improve thetransfer of heat to the feed/water admixture. At the closed-end top ofthe bell-shaped catalyst zone a reforming effluent outlet 206 isdisposed on the exterior wall 208 to remove the products of the steamreforming reaction from the bell-shaped catalyst zone. A fuel exhaustoutlet 204 is disposed at the top of the interior chamber space toremove the fuel exhaust stream from the interior chamber space.Preferably the fuel exhaust outlet is disposed at the top of theinterior chamber space in close proximity to the reforming effluentoutlet 206. To improve the contact of the feed/water admixture withinthe bell-shaped catalyst zone, a plurality of reactor surface extensions224 selected from the group consisting of fins, angled vanes,indentations, and combinations thereof are disposed on an inside surfaceof the exterior wall having an inside surface and an outside surface ofthe bell-shaped catalyst zone. The reactor surface extensions improvethe gas mixing at the wall within the catalyst zone. Preferably, thespacing between the surface extensions is equal to or greater than thepath length required to develop a heat transfer boundary layer.Similarly, a plurality of outer surface extensions 226 selected from thegroup consisting of fins, angled vanes, or indentations are disposed onthe outside surface of the exterior wall 208 of the bell-shaped catalystzone to improve the heat transfer between the exhaust gas stream and theexterior wall of the bell-shaped catalyst zone.

FIG. 4 illustrates an isometric sectional drawing of a shift reactionzone 300. The steam reforming effluent enters the shift reaction zone300 via conduit 301. The shift reaction zone 300 comprises a verticallyaligned series of water mixing zones and shift catalyst zones to produceadditional hydrogen and to reduce the amount of carbon monoxide in theshift reactor effluent. In one embodiment, shift reaction zone 300comprises a vertically aligned cylindrical vessel having an interiorspace. The cylindrical vessel has a shift inlet 302 at a top end of thevessel and a shift outlet 324 at a bottom end. As the reformer effluententers the shift inlet 302 the reformer effluent is passed to a firstwater spray zone 304 containing a water spray nozzle 304′ wherein thereformer effluent is contacted with a first water spray which isintroduced in line 310 to cool the effluent gases to effective hightemperature shift reaction conditions prior to passing the firsteffluent water admixture to the high temperature shift reaction zone 308and to produce a first effluent water admixture. The first effluentwater admixture is passed to a first dispersion zone 306 to provide morecomplete dispersion of the water in the effluent gases. The hightemperature shift reaction zone 308 contains a high temperature shiftcatalyst to produce a high temperature shift reactor effluent. The hightemperature shift reactor effluent is passed to a second water sprayzone 314 containing a second water spray nozzle 314′ to provide a secondwater effluent admixture to introduce more water via line 312 to coolthe high temperature shift reactor effluent to effective low temperatureshift reaction conditions. The second water effluent admixture is passedto a second dispersion zone 316 to provide uniform water distributionand then to the low temperature shift reaction zone 318. In the lowtemperature shift reaction zone 318 water or other coolant is passedthrough a coil 322 only in the event that the temperature rise acrossthe low temperature shift reaction zone 318 exceeds a desired marginsuch as 70° C. This maintains a means of maintaining the conversion ofthe low temperatures shift reaction zone 318 and the longevity of thecatalyst therein, independent of the operation of the high temperatureif shift reaction zone 308. The use of spray cooling as disclosed abovereduces the process thermal efficiency since the high-temperature heatcontained in the hot gases entering the shift reaction zones is used tovaporize water and can only be recovered at the condensation temperatureof the mixed stream thereby formed, which is too low for usefulrecovery. Although contrary to thermodynamic efficiency, the process hasthe advantages that heat transfer is very rapid, the cost of equipmentis greatly reduced compared with heat recovery by indirect heattransfer, and the amount of water carried by the gas is increased, whichprocesses the conversion of the shift reactors and the process hydrogenyield. The hydrogen product stream comprising hydrogen and less thanabout 3000 ppm carbon monoxide is recovered via shift outlet 324 andshift outlet conduit 328. Preferably, the hydrogen product stream issaturated with water.

EXAMPLES Example I

To prevent plume formation from the steam reforming zone, it isnecessary to heat the exhaust gas to a sufficient temperature to providetime for dispersion of the gas into the ambient air before the gas coolsto the dew point. The degree to which plume formation is likely can thusbe measured by the temperature difference between the exhaust gastemperature and the dew point temperature. Table 3 shows that if thecathode waste gas is discharged directly, separate from the burnerexhaust gas, then a plume forms. If the cathode waste gas is mixed withthe exhaust gas leaving the heat recovery exchanger, then thetemperature difference between the dew point and the exhaust temperatureis raised to 15° C.; however, if less than about 15% of the cathodewaste gas is fed to the process burner, then the temperature differenceis increased to 18° C., which provides a greater margin for dispersionand consequent reduction of plume formation.

TABLE 3 Cathode Exhaust Exhaust Gas With Molar Waste Gas Exhaust Gas 15%of CWG in Composition, Gas Without With All CWG Burner, Bal. (%) (CWG)CWG Blended at Exit Blended at Exit N₂ 46.6 62.4 51.8 49.3 O₂ 6.4 4.35.7 4.5 H₂O 47.0 22.7 39.0 42.4 CO₂ 0.0 10.6 3.4 3.7 Exhaust Temp., 80220 90 95.4 ° C. Dew Point, ° C. 80 65 75 77 T-T_(D) 0 155 18 18

Example II

The performance of the bell-shaped reaction zone wherein the exteriorand interior walls of the bell-shaped reaction zone are heated byconvection with the burner exhaust gases and radiation from the burnerflame is compared to a typical steam reforming reaction zone which isheated from only one side. The flue gas temperature of the burnerexhaust gases providing heat to the interior wall is about 800° C. Theinterior wall of each reactor which is closest to the burner is locatedabout 0.15 meters, radially from the burner and the catalyst bed widthis a constant value over the entire length of the catalyst zone. Radialtemperature profiles are developed at about 0.3, 3, 14, 43 and 100percent of the length of the catalyst bed. The fuel/water admixture ispassed to the catalyst zone at about 800° C. and a pressure of about 2bars with a steam-to-methane ratio of about 3, and a gas space velocityof about 2000 cubic meters of gas per cubic meters of catalyst per hour.The burner side of the interior wall is about 900° C. and the exhaustgas temperature is about 800° C. The methane conversion for the catalystzone heated from two sides is about 99% and the methane conversion for acatalyst zone heated from only one side is about 61 percent. The resultsof the comparison are shown in FIG. 5 for the reaction zone heated onone side and in FIG. 6 for the reaction zone heated on both the exteriorand interior walls. Clearly, in FIG. 5, the reactor outlet temperaturedoes not approach the inlet temperature as the feed is introduced to theendothermic reaction zone and results in a lower methane conversion. InFIG. 6, as the distance from the entrance of the reaction zoneincreases, the radial temperature in the bell-shaped reaction zoneapproaches a more uniform radial temperature profile with thetemperature at the outer, or exterior, wall approaching the temperatureof the interior wall. Table 4 shows the comparison of the averagetemperature of the effluent in the reactor at corresponding pointsthroughout the reactor bed. Clearly, when the outlet temperature of thecatalyst zone approaches the inlet temperature, the methane conversionis high and the methane slippage is significantly reduced.

TABLE 4 Comparison of Catalyst Zone Temperatures Length from Inlet ofBed, % Heating 2 Sides Heating 1 Side 0.3 512 506 3 542 515 14 611 53843 698 566 100 (Outlet) 804 602

Example III

The operation of the water gas shift reactor (WGSR) of the presentinvention as shown in FIG. 2 was simulated to illustrate the operatingof the reactor processing a feed stream produced by a steam reformingreactor. The results of the engineering simulation are shown in Table 5.A reforming effluent stream, or water gas shift feed stream,characterized as having about 56 mole percent hydrogen, about 10 toabout 12 mole percent carbon monoxide, and having a reformer outlettemperature of about 750° C., is first cooled by direct contact with afirst water stream at a water temperature of about 15° C. to about 40°C. in a first water spray zone to an effective high temperature shiftreaction temperature of about 450° C. The molar ratio of the feed streamto the first water spray is about 6:1, but could vary in a conventionalmanner depending upon the water temperature. The water/feed streamadmixture is passed to a first dispersion zone to disperse the water inthe water/feed stream admixture to avoid damage to the high temperatureshift catalyst in the high temperature shift reaction zone should coldwater contact the catalyst. The effluent from the high temperature shiftzone which exits the high temperature shift reaction zone at a hightemperature effluent temperature of about 475° C. is contacted with asecond water spray stream at a temperature of about 15° C. to form asecond admixture. The molar ratio of the high temperature shift effluentstream to the second water spray stream is about 5:1. This secondadmixture is passed to a second dispersion zone. The dispersed secondadmixture is passed to a low temperature shift reaction zone at a lowtemperature shift reaction temperature of about 200° C. to furtherreduce the carbon monoxide to a level less than about 3000 ppm-mol. Inthis Example III, the carbon monoxide in the low temperature shifteffluent stream is about 2500 ppm-mol and the low temperature shifteffluent, or outlet temperature is about 250° C.

TABLE 5 Operation of Water Gas Shift Reactor Steam First High Second LowRe- Water Temperature Water Temperature forming Spray Shift Spray ShiftEffluent Stream Effluent Stream Effluent Temperature, 750 15 475 15 250° C. Pressure, kPa 150 190 145 190 140 Composition, mol-% Hydrogen 55.649.7 47.1 Carbon 10.2 6.3 0.255 Monoxide Carbon 6.3 7.68 11.6 DioxideMethane 0.27 0.23 0.19 Water 27.7 100 36.1 100 40.9

What is claimed is:
 1. An apparatus for generating hydrogen for producing electric power from a fuel cell, said apparatus comprising: a) a substantially closed outer vessel defining an interior chamber and comprising insulated walls, a top and a base; b) an inner vessel within the interior chamber having a dome shape and being vertically aligned having an open-end base and a closed-end top, said inner vessel being defined by one or more hollow walls having a middle space within said one or more hollow walls, wherein a compartment for retaining catalyst is provided by said middle space and wherein said inner vessel surrounds a combustion zone; c) a burner fixed to the base and positioned within said combustion zone to provide a flame zone and an anode waste gas conduit disposed in the combustion zone to provide injection of anode waste gas into the flame zone; d) a burner tube fixed to the base and extending vertically above the base to surround the burner; e) a feed distributor fixed to said inner vessel and defining a plurality of ports distributed about the open-end bottom in fluid communication with the compartment; f) a feed conduit in fluid communication with the feed distributor; g) a reforming effluent outlet about the closed-end top of the inner vessel and in fluid communication with said compartment; and h) a fuel exhaust outlet about the top of the outer vessel.
 2. The apparatus of claim 1 further comprising a fuel conduit and an air conduit in fluid communication with said burner.
 3. The apparatus of claim 1 further comprising an extended heat transfer surface on an outside surface of a portion of said feed conduit located in said interior chamber.
 4. The apparatus of claim 1 further comprising an extended heat transfer surface disposed within the one or more hollow wall.
 5. The apparatus of claim 1 further comprising an extended heat transfer surface disposed on an outside surface of said inner vessel. 